From: Noah Misch <noah@leadboat.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Heath Lord <heath.lord@crunchydata.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: "could not reattach to shared memory" on buildfarm member dory
Date: Tue, 25 Sep 2018 08:05:12 -0700
Message-ID: <20180925150512.GA3990982@rfd.leadboat.com> (raw)
In-Reply-To: <14554.1537811585@sss.pgh.pa.us>
References: <20180423231855.GK27724@tamriel.snowman.net>
<CAEepm=0kRF7Hrd2R72FJLdQneV1HATjJM_ArbjZw=-ZF3RT7+Q@mail.gmail.com>
<20180424070646.GA2693533@rfd.leadboat.com>
<17897.1525108069@sss.pgh.pa.us>
<29823.1525132900@sss.pgh.pa.us>
<20180501002419.onmikldoe2ssjauq@alap3.anarazel.de>
<18056.1525148010@sss.pgh.pa.us>
<22096.1525188710@sss.pgh.pa.us>
<20180819020007.GD3795674@rfd.leadboat.com>
<14554.1537811585@sss.pgh.pa.us>
On Mon, Sep 24, 2018 at 01:53:05PM -0400, Tom Lane wrote:
> Noah Misch <noah@leadboat.com> writes:
> > In this proof of concept, the
> > postmaster does not close its copy of a backend socket until the backend
> > exits.
>
> That seems unworkable because it would interfere with detection of client
> connection drops. But since you say this is just a POC, maybe you
> intended to fix that? It'd probably be all right for the postmaster to
> hold onto the socket until the new backend reports successful attach,
> using the same signaling mechanism you had in mind for the other way.
It wasn't relevant to the concept being proven, so I suspended decisions in that
area. Arranging for socket closure is a simple matter of programming.
> Overall, I agree that neither of these approaches are exactly attractive.
> We're paying a heck of a lot of performance or complexity to solve a
> problem that shouldn't even be there, and that we don't understand well.
> In particular, the theory that some privileged code is injecting a thread
> into every new process doesn't square with my results at
> https://www.postgresql.org/message-id/15345.1525145612%40sss.pgh.pa.us
>
> I think our best course of action at this point is to do nothing until
> we have a clearer understanding of what's actually happening on dory.
> Perhaps such understanding will yield an idea for a less painful fix.
I see.
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To: pgsql-hackers@postgresql.org
Cc: noah@leadboat.com, tgl@sss.pgh.pa.us, heath.lord@crunchydata.com, andres@anarazel.de, thomas.munro@enterprisedb.com, sfrost@snowman.net, pgsql-hackers@lists.postgresql.org
Subject: Re: "could not reattach to shared memory" on buildfarm member dory
In-Reply-To: <20180925150512.GA3990982@rfd.leadboat.com>
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